The development of effective asymmetric reactions that enable the enantioselective formation of one chiral center over another continues to be an important area of research. One such asymmetric reaction involves the introduction of a chiral center into a molecule through the enantioselective hydrogenation of a prochiral unsaturated bond by using a transition metal catalyst bearing chiral organic ligands. Numerous chiral phosphine catalysts have been developed to enantioselectively introduce chiral centers to prochiral olefins, carbonyls and imines with high enantiomeric excess. One such class of chiral catalysts employs the chiral phosphine ligand 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (hereinafter referred to as "BINAP").
A second important area of research relates to the development of water-soluble organometallic catalysts. Conventionally, catalytically active organometallic complexes have been applied as homogeneous catalysts in solution in the organic reaction phase. Difficulties associated with recovery of the homogeneous catalysts from the reactants and products diminish the utility of these homogeneous catalysts, especially when the cost of the catalyst is high or where there is the need to isolate the reaction products in high purity.
One mode in which water soluble organometallic catalysts have been used is in two phase systems comprising an aqueous phase and a water immiscible phase (e.g. ethyl acetate--water). Separation of the organometallic catalyst from organic reactants and products is greatly simplified due to the insolubility of the catalyst in the water immiscible phase. However, in some instances, the utility of the two phase system has been limited by a lack of substrate and/or reactant solubility in the aqueous phase, by the limited interfacial area between the two phases, and by poor selectivity.
Supported phase (SP) organometallic catalysts have been developed to overcome some of the shortcomings associated with two phase reaction systems. In a supported phase system the interfacial area between the support phase, which contains the organometallic catalyst, and the water immiscible (bulk organic) phase, is greatly enhanced.
The advantages of supported phase organometallic catalyst systems have prompted further investigation into catalyst systems which will retain the beneficial characteristics thereof while further increasing yield and enantioselectivity.